首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2788篇
  免费   192篇
  国内免费   243篇
化学   445篇
晶体学   3篇
力学   190篇
综合类   23篇
数学   1936篇
物理学   626篇
  2024年   5篇
  2023年   27篇
  2022年   32篇
  2021年   63篇
  2020年   75篇
  2019年   79篇
  2018年   82篇
  2017年   74篇
  2016年   74篇
  2015年   63篇
  2014年   132篇
  2013年   259篇
  2012年   92篇
  2011年   133篇
  2010年   109篇
  2009年   143篇
  2008年   170篇
  2007年   163篇
  2006年   168篇
  2005年   131篇
  2004年   127篇
  2003年   144篇
  2002年   132篇
  2001年   75篇
  2000年   102篇
  1999年   91篇
  1998年   85篇
  1997年   58篇
  1996年   40篇
  1995年   33篇
  1994年   33篇
  1993年   26篇
  1992年   23篇
  1991年   25篇
  1990年   15篇
  1989年   16篇
  1988年   15篇
  1987年   12篇
  1986年   8篇
  1985年   23篇
  1984年   8篇
  1983年   10篇
  1982年   12篇
  1981年   6篇
  1980年   6篇
  1979年   5篇
  1978年   4篇
  1977年   3篇
  1976年   4篇
  1973年   3篇
排序方式: 共有3223条查询结果,搜索用时 203 毫秒
1.
2.
This paper is dedicated to studying the following Schrödinger–Poisson system Δ u + V ( x ) u K ( x ) ϕ | u | 3 u = a ( x ) f ( u ) , x 3 , Δ ϕ = K ( x ) | u | 5 , x 3 . Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions.  相似文献   
3.
4.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data.  相似文献   
5.
We formulate and discuss a reduction theorem for Poisson pencils associated with a class of integrable systems, defined on bi-Hamiltonian manifolds, recently studied by Gel'fand and Zakharevich. The reduction procedure is suggested by the bi-Hamiltonian approach to the separation of variables problem.  相似文献   
6.
For a discrete linear stochastic dynamical system, computation of the response matrix to the external action from a subspace using given observational data is examined. An algorithm is proposed and substantiated that makes it possible to improve the numerical accuracy and to reduce the amount of observational data compared to the general case where an arbitrary external action is allowed. As an illustration, a discrete system arising in the analysis of a linear stochastic dynamical continuous-time system is considered more thoroughly. Some numerical results are presented.  相似文献   
7.
Software failures have become the major factor that brings the system down or causes a degradation in the quality of service. For many applications, estimating the software failure rate from a user's perspective helps the development team evaluate the reliability of the software and determine the release time properly. Traditionally, software reliability growth models are applied to system test data with the hope of estimating the software failure rate in the field. Given the aggressive nature by which the software is exercised during system test, as well as unavoidable differences between the test environment and the field environment, the resulting estimate of the failure rate will not typically reflect the user‐perceived failure rate in the field. The goal of this work is to quantify the mismatch between the system test environment and the field environment. A calibration factor is proposed to map the failure rate estimated from the system test data to the failure rate that will be observed in the field. Non‐homogeneous Poisson process models are utilized to estimate the software failure rate in both the system test phase and the field. For projects that have only system test data, use of the calibration factor provides an estimate of the field failure rate that would otherwise be unavailable. For projects that have both system test data and previous field data, the calibration factor can be explicitly evaluated and used to estimate the field failure rate of future releases as their system test data becomes available. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
8.
Given a principal value convolution on the Heisenberg group Hn = Cn×R, we study the relation between its Laguerre expansion and the Fourier-Bessel expansion of its limit on Cn. We also calculate the Dirichlet kernel for the Laguerre expansion on the group Hn.  相似文献   
9.
The pure state space of Quantum Mechanics is investigated as Hermitian Symmetric Kähler manifold. The classical principles of quantum mechanics (Quantum Superposition Principle, Heisenberg Uncertainty Principle, Quantum Probability Principle) and Spectral Theory of observables are discussed in this non-linear geometrical context.  相似文献   
10.
Modulo some natural generalizations to noncompact spaces, we show in this Letter that Moyal planes are nonunital spectral triples in the sense of Connes. The action functional of these triples is computed, and we obtain the expected result, i.e. the noncommutative Yang–Mills action associated with the Moyal product. In particular, we show that Moyal gauge theory naturally fits into the rigorous framework of noncommutative geometry.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号